Diabetic Ketoacidosis (DKA) or Undiagnosed Diabetes Mellitus: Although the patient has no history of elevated glucose, the presence of ketones and protein in the urine, along with urinary frequency, suggests a possible diagnosis of undiagnosed diabetes mellitus or DKA. This condition can present at any age, and symptoms can sometimes be subtle or attributed to other causes, especially in older adults.

Urinary Tract Infection (UTI): UTIs can cause urinary frequency and the presence of protein or ketones if the infection is severe or if there is an associated condition like sepsis. Elderly individuals may not always present with typical symptoms.
Chronic Kidney Disease (CKD): CKD can lead to proteinuria and may be associated with metabolic disturbances that could result in ketonuria. The urinary frequency could be due to decreased renal concentrating ability.
Prostate Issues (e.g., Benign Prostatic Hyperplasia - BPH): While BPH itself might not directly cause ketones or protein in the urine, it can cause urinary frequency and, if complicated by a UTI or other conditions, could potentially lead to the findings described.

Kidney Stones: Although less likely to cause ketones, kidney stones can cause severe pain, urinary frequency, and potentially protein or blood in the urine. A stone causing obstruction could lead to infection or other complications.
Malignancy (e.g., Bladder or Kidney Cancer): These conditions can cause a variety of urinary symptoms, including frequency, and may be associated with metabolic disturbances or paraneoplastic syndromes that could explain the ketones and protein.

Primary Amyloidosis: This condition can cause proteinuria due to kidney involvement but would be an uncommon cause of the combination of symptoms described.
Familial Dyslipidemias: Certain rare genetic disorders affecting lipid metabolism could potentially lead to ketosis, but these would be unusual causes of the patient's presentation.

Immediate: Check blood glucose levels, complete blood count (CBC), blood urea nitrogen (BUN), creatinine, and electrolyte panel to assess for DKA, UTI, or acute kidney injury.
Urine Culture: To rule out UTI.
Imaging: Ultrasound of the kidneys and bladder to evaluate for obstruction, stones, or masses.
Glucose Monitoring: Continuous glucose monitoring or repeated glucose measurements to diagnose diabetes.
Treatment will depend on the diagnosis:
- DKA or Diabetes: Insulin therapy, fluid replacement, and management of electrolyte imbalances.
- UTI: Antibiotics.
- CKD: Management of underlying conditions, dietary adjustments, and potential referral to a nephrologist.
- Prostate Issues: Medications for BPH, or surgical intervention if necessary.
- Kidney Stones: Pain management, hydration, and potential intervention for stone removal.
- Malignancy: Referral to an oncologist for appropriate staging and treatment.